Sam never moves into Bag End in the movie, perhaps because in the few scenes they had to work with, they wanted to show Frodo alone and withdrawn ("How do you pick up the threads of an old life?"), wandering around in that empty, echoing, unnaturally tidy Bag End.

I figure we're meant to imagine that the Sackville-Bagginses inherit Bag End after Frodo leaves, and that Sam never gave up his simple life as a gardener or his humble hobbit-hole. There's a certain bitter-sweetness to that, really - different from Tolkien's imagined rise in social status for Sam and family, but then Sam never takes over from Frodo as the "true hero" of the story in the film as he does in the book. And the social status thing is much less important in the films anyway - Sam doesn't need a big imposing home to show he's grown in stature, I think it's that moment when he leaves the other hobbits and goes up to make his move on Rosie that tells us he's not the shy, retiring hobbit he used to be!

They went in, and Sam shut the door. But even as he did so, he heard suddenly, deep and unstilled, the sigh and murmur of the Sea upon the shores of Middle-earth. From the unpublished Epilogue to the Lord of the Rings